Valmiki Ramayana Bala Kanda Sarga 43 Shloka 5
Original Shlokaअचिन्तयच्च सा देवी गङ्गा परमदुर्धरा।।1.43.5।। विशाम्यहं हि पातालं स्रोतसा गृह्य शङ्करम्।
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परमदुर्धरा extremely difficult to contain, सा देवी that goddess, गङ्गा Ganga, अचिन्तयच्च also thought over, अहम् I, स्रोतसा by my flow, शङ्करम् Siva, गृह्य seizing, पातालम् lower regions of earth, विशामि I shall enter.
"Goddess Ganga, extremely difficult to contain, thought that seizing Siva with her flow she would enter the lower regions of the earth.